The main objectives of the proposed research are: to elucidate the biochemical site(s) of action of the dialdehyde derivatives of nucleosides and nucleotides which result in inhibition of tumor cell growth; to determine the specificity of this inhibition of nucleic acid synthesis in tumor cells; and to specifically direct these studies to the compound In x (NSC-118994) since it has been started on Phase I clinical trials. These studies will be carried out on enzymes involved in nucleotide metabolism and nucleic acid synthesis in cell-free extracts, in intact tumor cells in culture and on tumor growth in vivo.